This invention basically relates to the field of machinery. It is specially related to a contactless and digital measuring method of the linear or angular condition of one piece with respect to another piece, these two pieces being movable in relation to each other, based on the reading of a metallic encoding pattern detectable by a magnetic reading device fixed on one of the two pieces.
The invention further contemplates a device for implementing the method, and a method for the manufacture of the device.
Similar measuring devices are already known. Thus, published EP-A1-0,027,308 discloses a magnetic scale for measuring a displacement, comprising a locally magnetized magnetic substrate. French patent FR-A-2,030,713 describes a well known non-metallic and conventional magnetic tape including spaced magnetic information for measuring. An information bulletin (IBM Vol. 6 no. 2 of Jul. 1963) mentions that non-magnetic nickel coated with kanigan can be rendered magnetic by heating to about 400.degree. C. German publication DE-A1-1,623,242 discloses a measuring system based on the detection of a continuously growing magnetic field in linear direction. Finally, European publication EP-A1-0,310,543 discloses a magnetic pattern on a magnetic substrate, the magnetic force of the pattern being different form that of the substrate.
All devices already proposed and suggested have the common disadvantage that the shape and intensity of the finally obtained measuring signal and its sharpness with respect to the non-encoded environment or substrate are by far not satisfactory. Conventional tapes cannot be used in the severe conditions of machinery.